buy like 3 of these if you're serious about your Glock. It's durable (trust me, I drop my mags COUNTLESS times) and feed just right %99 of the time (C'mon, all mags jam up one or twice before they're retired!).
Great mag. it holds 30 rounds and does its job well. my only problem with it is it sometimes sprays its bbs when in a pouch if it is nudged in the little metal endpiece.